The present invention relates to a color cathode ray tube, and more particularly to a color cathode ray tube capable of facilitating the reliable internal graphite coating operation and reducing the power consumption of a deflection yoke.
In general, a cathode ray tube which is employed as an image display device is constituted by a vacuum envelope which is formed by connecting a panel portion which forms a screen by coating a phosphor on an inner surface thereof, a neck portion which accommodates an electron gun, and a funnel portion in a funnel shape which gradually reduces the diameter thereof in the direction from the panel portion to the neck portion.
In a color cathode ray tube, a color screen to which a plurality (usually three colors) of phosphors are coated is provided to an inner surface of a panel portion, a shadow mask which works as a color selection electrode is arranged adjacent to the screen, and an inline-type electron gun which irradiates three electron beams is accommodated in a neck portion.
The color cathode ray tube includes a stem at the end of the neck portion, wherein the stem supports the accommodated electron gun and allows stem pins which supply a given voltage or given signals to the electron gun to pass therethrough for mounting thereof to be mounted in an annular manner thus sealing the neck portion. A deflection yoke which reproduces an image on the screen by deflecting the electron beams in both horizontal and vertical directions is mounted on the outer surface of the funnel portion.
A color display tube (CDT) used as a monitor device of an information processing terminal is used with a higher deflection frequency than a conventional cathode ray tube for television and hence, the deflection power is increased.
In such a cathode ray tube, as a means for reducing the power consumed by the deflection yoke, the outer diameter size of a portion on which the deflection yoke of the funnel is mounted (deflection yoke mounting region) may be made small so as to make the deflection yoke approach to the electron beams thus efficiently applying the deflection magnetic field to the electron beams.
However, in case the outer diameter of the deflection yoke mounting region is simply made small, a portion of the funnel portion connected to the neck portion (smaller diameter portion of the funnel portion) becomes narrow and hence, at the time that the electron beams take the maximum deflection angle, the electron beams impinge on the inner wall of the funnel portion thus giving rise to a region on the phosphor screen where the electron beams do not reach (non-scanned portion).
In view of such a fact, Japanese Laid-Open Patent Publication Hei 10-144238/1998 discloses a cathode ray tube which forms an outer wall of a deflection yoke mounting region of the funnel portion in a pyramidal shape so as to narrow the distance between the deflection yoke and the electron beams and to avoid the occurrence of a non-scanned portion. However, in case the outer wall of the deflection yoke mounting region is formed in the pyramidal shape, the mechanical strength of the vacuum envelope is weakened and hence, a possibility that a so-called implosion occurs is increased. In the above-mentioned Japanese Laid-open Publication Hei 10-144238/1998, to prevent the occurrence of the implosion, a reinforcing member is mounted on a connecting portion between the pyramidal-shaped deflection yoke mounting region and the panel portion. The cathode ray tube disclosed in this publication has a cross section of an outer wall thereof in a direction perpendicular to the tube axis of the deflection yoke mounting region formed in a rectangular shape and a cross section of an inner wall thereof also formed in a similar rectangular shape.
Further, Japanese Utility model Publication Sho 44-29152/1969 discloses a cathode ray tube in which to eliminate a non-scanned portion on a connecting region between the funnel portion and the neck portion (narrow-diameter portion of the funnel portion) which is caused by the enlargement of the deflection angle of the cathode ray tube, and to obviate the implosion, the opening shape of the inner wall (cross section of inner wall in a direction perpendicular to the tube axis) of the portion where the diameter of the funnel portion is narrowed is formed such that bulges which protrude inwardly are formed (in a so-called pin-cushion shape) on given portions of all of or two parallel sides out of four sides which form the profile line, and the corners are rounded.
In this type of cathode ray tube, a so-called internal graphite film is coated on an approximately entire surface of of the inner wall of the funnel portion and the neck portion connected to the funnel portion. This internal graphite film has a function of supplying a high voltage applied to an anode button which is mounted by passing through the large-diameter wall surface of the funnel from the front to the back thereof to an anode electrode of the electron gun.
This internal graphite film is formed before the panel portion is connected to the funnel portion such that a coating liquid which disperses graphite particles in a solvent is coated to the inner surface of the funnel portion and then is dried. That is, the funnel is rotated in a condition that the funnel is vertically installed with a side of a large diameter to which the panel portion is connected directed upwardly and the neck portion side directed downwardly and the internal graphite is coated by means of an automatic brush coating machine.
In this internal graphite coating operation, the inner wall of the large-diameter portion of the funnel portion is formed of a substantially flat wall and hence, problems such as the uneven coating or the liquid well do not occur. In the deflection yoke mounting region, however, the cross section of the inner wall is narrow and hence, problems such as the uneven coating of the graphite coating liquid, the liquid well, or the sagging of liquid in the tubular inside of the neck portion are liable to occur.
Particularly, in a case as disclosed in Japanese Utility model Publication Sho 44-29152/1969 where the opening shape of the inner wall of the deflection yoke mounting region is formed such that given portions of all or opposing two sides out of four sides which constitute the profile of the opening are provided with bulges which protrude inwardly to form a pin-cushion shape, a brush cannot smoothly come into contact with the inner wall surface and hence, the uneven coating occurs at four corners or the coating liquid well occurs thus deteriorating the reliability of the cathode ray tube.
Although the above-mentioned prior art discloses the prevention of the occurrence of the non-scanned portion due to the increase of the deflection angle and the enhancement of the mechanical strength of the vacuum envelope, the prior art neither discloses nor suggests the problems which occur in the internal graphite film coating operation.
The color cathode ray tube of the present invention includes a vacuum envelope comprised of a panel portion having an approximately rectangular shape which forms a phosphor film on an inner surface thereof, a neck portion which accommodates an electron gun, and a funnel portion which connects the panel portion and the neck portion, wherein an outer wall cross section of a deflection yoke mounting region of the funnel portion in a direction perpendicular to the tube axis is formed in an approximately rectangular shape, and an inner wall cross section is formed in an approximately pin-cushion shape, which has curvatures for forming recesses at corner portions. The respective corner portions have inwardly indented curvatures, and the difference between a first straight line which connects neighboring bottom portions of said the corners and a second straight line which is in contact with a central point of the inner wall between the neighboring corner portions and is disposed parallel to the first straight line is set to 2.0 mm at maximum and preferably not more than 1.0 mm provided that the direction toward the tube axis is taken as +, and the outer diameter of the neck portion is set to not more than 25.3 mm.
Further, in the cathode ray tube of the present invention, the shapes of the outer wall cross sections taken in a direction perpendicular to the tube axis within a range covering 35 mm toward the panel portion side and 20 mm toward the neck portion side from a reference line set in the deflection yoke mounting region of the funnel portion is formed in a rectangular shape and the inner wall cross sections is provided with pin-cushion shape portions which have curvatures to form recesses at corners of the inner wall.
The cathode ray tube of the present invention includes a vacuum envelope which is comprised of an approximately rectangular shape which forms a three-color phosphor film on an inner surface thereof, a neck portion which accommodates an inline type electron gun and a funnel portion which connects the panel portion and the neck portion. The cathode ray tube includes a deflection yoke mounting region at a transition region between the funnel portion and the neck portion. At a reference line set in the deflection yoke mounting region of the funnel portion, the shape of an outer wall opening and the shape of an inner wall opening in a direction perpendicular to a tube axis are respectively formed in an approximately rectangular shape and in an approximately barrel shape, and in case a radius of curvature of the outer wall cross section of the deflection yoke mounting region is set to R1 (mm) and a radius of curvature of the inner wall cross section of the deflection yoke mounting region is set to R2 (mm), the relationship between the radii R1 and R2 is determined such that R1xe2x89xa7100 mm and R2xe2x89xa7R1, and the outer diameter of the neck portion is not more than 25.3 mm.
Here, the reference line set in the deflection yoke mounting region of the funnel portion is positioned at the central portion of the deflection yoke mounting region in the tube axis direction and this position is defined by EIAJ ED-2134.
Due to the above-mentioned constitutions, the internal graphite film coating operation in the deflection yoke mounting region can be carried out smoothly and the formation of the irregular film thickness due to the uneven coating or the liquid well, or the sagging of coating liquid in the tubular inside of the neck portion can be avoided and hence, a cathode ray tube which can obtain the high reliability and can reduce the deflection power is realized.